Research Of Testing Methods Of Capacitive Current For Medium Voltage Grid

In recent years, the expansion of distribution power network and the large use of cables make the capacitive current reach a higher level.When the single-phase grounding occurs, the fault point exists large capacitive current.Excessive capacitance current easily generates arc which causes arc over-voltage.Arc over-voltage damages the insulation of the weak part.When the capacitive current exceeds the set value in the distribution network, arc suppression coil should be installed to make the grounding arc die out quickly and avoid the expansion of accident. Therefore, in order to mitigate danger the capacitance current of distribution network 、 to determine the system operation mode 、 to determine whether the arc suppression coil should be installed and the capacity of arc suppression coil,the capacitance current of distribution network needs to be accurately measured.The measuring methods of the existing capacitance current are studied and different measuring methods are simulated in this paper. Meanwhile the advantages and disadvantages of the methods mentioned above and the accuracy of measurement are analyzed.Vector method with more advantages is adopted and studied deeply.And the selection of the injected signal is analyzed.Research shows that the reasonable choice of the frequency range and injected signal strength can reduce the error of measurement.Based on the theoretical analysis,’a high and a low’ frequency are chosen and injected.Asymmetric system with white noise、 electric arc furnace and converter model is built in the simulation system.And the effects with nonlinear load and unbalanced system on vector methods are analyzed.Finally, the signal extraction of signal injection method is studied.An IIR filter is designed to be used to extract the signal from the signal containing noise and 50 Hz frequency interference.Simulation results shows that the IIR filter has high accuracy to extract the signal, which can make the capacitive current measurement results with high precision.